Software access point
A software access point is used when you want your computer to act as an access point for the local wireless network. It saves you the trouble of getting a separate wireless router.
Overview and Requirements
Setting up an access point comprises two main parts:
- Setting up the link layer, so that wireless clients can associate to your computer's "software access point" and send/receive IP packets from/to your computer; this is what the hostapd package will do for you
- Setting up the network configuration on you computer, so that your computer will properly relay IP packets from/to its own Internet connection from/to wireless clients.
The second point is actually the more complicated one, and there's two basic ways for implementing it:
- bridge: create a network bridge on your computer (wireless clients will appear to access the same network interface and the same subnet that's used by your computer)
- NAT framework: with IP forwarding/masquerading and DHCP service (wireless clients will use a dedicated subnet, data from/to that subnet is NAT-ted -- similar to a normal WiFi router that's connected to your DSL or cable modem)
The bridged approch is more simple, but it requires that any service that's needed by your wireless clients (like, DHCP) is available on your computers external interface. That means it will not work if you have a dialup connection (e.g., via PPPoE or a 3G modem) or if you're using a cable modem that will supply exactly one IP address to you via DHCP.
The NAT aproach is more versatile, as it clearly separates wifi clients from your computer and it's completely transparent to the outside world. It will work with any kind of network connection, and (if needed) you can introduce traffic policies using the usual iptables approach.
So, what you will need is:
- For the actual Wifi link layer:
- prism2/2.5/3 pure pci wireless card or nl80211 compatible cards (e.g. ath9k)
- wireless_tools, hostapd from pacman
- For the network setup:
- either bridge-utils (for the bridged setup), or
- iptables and dnsmasq (or dhcp) from pacman
Steps to implement
Wifi Link Layer
The actual Wifi "link" -- including WPA2 authentication -- is established via the hostapd package.
The config file of hostapd /etc/hostapd/hostapd.conf will help you to put your wireless device into master mode and willing to accept connection from other computers with encrypted password.
Here is an example from http://www.su-root.co.uk/computing/turn-your-linux-computer-in-a-wireless-access-point-using-hostapd:
interface=wlan0 # must match your wifi interface # bridge=br0 # uncomment only for the bridged setup driver=nl80211 # change if necessary logger_stdout=-1 logger_stdout_level=2 ssid=test # set to desired WiFi network name hw_mode=g channel=6 auth_algs=3 max_num_sta=255 # max number of clients wpa=2 # use WPA2 wpa_passphrase=tryyourbest wpa_key_mgmt=WPA-PSK wpa_pairwise=TKIP CCMP rsn_pairwise=CCMP
For automatically starting hostapd, add it to the DAEMONS array in the rc.conf file:
... DAEMONS=( ... hostapd ... ) ...
Bridged Setup with Kernel >= 2.6.33)
Due to changes in the kernel since version 2.6.33 bridges cannot contain an uninitialized interface. Because of this we need hostapd to add the wlan interface to the bridge instead.
- kernel >= 2.6.33
- hostapd >= 0.7.1
Setup a profile in /etc/network.d/ (for example called "bridge").
INTERFACE="br0" CONNECTION="bridge" DESCRIPTION="Bridge wired and wireless connection" # Only add wired interface here, hostapd will add wireless BRIDGE_INTERFACES="eth0" IP="dhcp"
In rc.conf make sure you do the following:
- Add the bridge profile to the NETWORKS list.
- Make sure you are starting the profiles by adding net-profiles to the DAEMONS list.
- Start hostapd after net-profiles by adding it to the DAEMONS list.
NETWORKS=( bridge ) ... DAEMONS=( ... net-profiles hostapd ... )
Reboot the machine and use another computer to see if you can find the "test" wireless connection.
If you do not want to reboot these commands should work:
netcfg up bridge rc.d start hostapd
Old way to set up bridge
before hostapd does its job, eth0, wlan0 and br0 must be up and do not have any address. we can put the following lines in /etc/rc.conf
eth0="eth0 up" wlan0="wlan0 up" br0="br0 192.168.0.2 netmask 255.255.255.0 up" INTERFACES=(lo eth0 wlan0 br0)
in the /etc/conf.d/bridges file, uncomment the lines (change eth1 to wlan0)
bridge_br0="eth0 wlan0" BRIDGE_INTERFACES=(br0)
we are ready to go, just reboot the machine and use another computer to see if you can find the "test" wireless connection.
The description below assumes that
- network 192.168.0.x is used for the Wifi network
- your computer acts as default gateway for that network (on 192.168.0.1), and
- hostapd is attached to interface wlan0
- your computer's internet connection is via ppp0
If you need to use a different subnet, or if your device names are different, then please change the examples below accordingly.
Step 1: IP Configuration
Ensure that hostapd is running (run /etc/rd.c/hostapd start). Then perform these commands:
ifconfig wlan0 192.168.0.1 # assign IP address to interface used by hostapd sysctl net.ipv4.ip_forward=1 # enable IP forwarding iptables -P FORWARD ACCEPT # initialize iptables chains iptables -P OUTPUT ACCEPT iptables -P INPUT ACCEPT iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -o ppp0 -j MASQUERADE # setup NAT
This will establish proper IP forwarding and NAT for all WiFi clients that connect via hostapd. For more advanced configuration, or if you need to setup NAT with an existing forewall, see Simple stateful firewall.
What's missing still is a DHCP service so clients can automatically acquire the needed settings.
Step 2: DHCP Server
While any DHCP server will do (like the dhcp package from pacman), the description here is based on the dnsmasq package; it is easier to configure and it provides caching for DNS queries coming from WiFi clients.
Install the dnsmasq package:
pacman -S dnsmasq
Uncomment this line in /etc/dnsmasq.conf:
... conf-dir=/etc/dnsmasq.d ...
Create the DHCP config for dnsmasq in a new file /etc/dnsmasq.d/dhcpd
Then start dnsmasq by running
At this points, WiFi clients should be able to connect to your network, then acquire the network config via DHCP, and then send/receive data using your computer as a NATted router.